Switching regulators with half-bridge circuits commonly use a bootstrap circuit having a diode and a bootstrap capacitor connected in series. The bootstrap circuit is typically connected to a node between a high-side transistor and a low-side transistor. To minimize chip size, the size of the bootstrap capacitor is kept small, thereby also keeping the capacitance small. With the reduced capacitance of the bootstrap capacitor, the power consumption of the floating logic being supplied by the bootstrap capacitor becomes more relevant. Ideally, to alleviate the problems associated with a small bootstrap capacitance, the charge stored in the boot strap capacitor should be maximized and the power consumption of the logic circuits supplied by the bootstrap capacitor should be minimized.
The charge stored in the boot strap capacitor can be increased if the diode connected between the supply voltage and the bootstrap capacitor is replaced by a device having a lower voltage drop than a silicon diode. For this reason it is known to employ a Schottky diode instead of a silicon diode. However, this approach is unfavorable, because when using common chip fabrication processes Schottky diodes cannot be easily integrated and so have to be realized as an external component.
For various reasons, the high-side transistor is not driven directly by a level-shifted version of an input signal, but rather via a floating latch which is turned on and turned off by short pulses. In order to reduce a degradation of the signal due to noise, low resistor values are used in the level-shifter resulting in a high load of the bootstrap capacitor. The average load of the bootstrap capacitor can be reduced by triggering only short pulses which are then level shifted. This level shifted pulses trigger the floating latch, thus restoring the signal controlling the switching state of the high-side switch.
There is a general need for a circuit arrangement and for a method for driving a high-side transistor. Such a circuit arrangement may allow for a relatively simple solution which may provide a fail-safe operation without the necessarily using additional refresh circuits, and may further allow integration into a single chip without necessarily using external components.